Many different types of presses are currently in use. Presses may incorporate a stationary upper member and a vertically translatable lower member, or a stationary lower platen and a vertically translatable upper platen. Pressure, which may be considerable pressure, may be used to urge the lower platen vertically upward to the upper platen. In some applications heat may also be applied to one or more of the mating platen surfaces to effect a particular operation. Once the operation is concluded the pressure is typically relieved and the lower platen is allowed to return to its original position, spaced from the upper platen.
A variety of different types of safety hazards may exist in connection with the operation of presses. One concern relates to the possibility that a user or other observer may place a hand or other body member within the space between upper and lower platens. Many industrial machines accommodate such a potential hazard by inclusion of dual start switches, on the machine. In order for the lower platen to begin upward movement, the operator must almost simultaneously within less than 1 second of each other depress both start switches, which are spaced from each other sufficient to require two hand operation. Thus, the operator's hands are necessarily removed from the area intermediate the upper and lower platens as the machine begins to operate. While this technique is generally effective, operators have occasionally found ways to defeat the safety mechanisms, such as by taping one switch into an on position to allow the use of that hand to manipulate products between the platens while the second switch is being depressed.
Moreover, even where the dual start switches are properly used, they do not provide any safety benefit in the event that an observer intentionally or inadvertently reaches into the operating area after the start switches have been activated. Accordingly, there remains a need to develop a further safety mechanism for use in connection with presses, which operate independent of electronic control systems that can be defeated or ineffective under certain circumstances.
Another shortcoming of existing press safety techniques concerns the retraction, or downstroke, of the lower platen. While start switches are generally effective to avoid injury during the upstroke, they are commonly not useful to avoid injury during the downstroke, which may occur automatically when the operator's hands are removed from the start switches. Put otherwise, once the press cycle is initiated by depression of the start switches, the cycle may continue to completion, despite the fact that the switches are released. As a consequence, the operator may extend a hand or other body member within the area between the machine base and the lower platen, causing injury as the lower platen, causing injury as the lower platen lowers to its original position. While some lower platens are formed to be vertically separable from the drive mechanism, the close engagement of the two may result in a locking relationship when any obstruction causes tilting of the lower platen from its normal horizontal position. As a consequence, the lower platen may not in fact separate from the drive mechanism during the downstroke, which may result in compressing or crushing any body member caught between the lower platen and the machine base.
The present invention is directed to a mechanism which addresses these and other problems, providing significant safety enhancements to the operation of presses, which are independent of electronic control systems and are unlikely to be defeated.